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How do I attemp such a Question?

  1. Jan 27, 2006 #1
    :confused: Can someone please help me?

    A horizontal string can transmit a maximum power (without breaking) if a wave with amplitude A and angular frequency is travelling along it. To increase this maximum power, a student folds the string and uses this "double string" as a medium. Determine the maximum power that can be transmitted along the "double string" assuming that the tension is constant.
  2. jcsd
  3. Jan 27, 2006 #2


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    Science Advisor
    Homework Helper

    You should really show some of your own work and ideas before asking a question in the homework section but I'll give you a hint: While the tension remains the same, both the length and the mass per unit length change. :)
  4. Jan 29, 2006 #3
    If the string is being folded would its mass per unit length double and its length would decause by 1/2?
  5. Feb 3, 2006 #4
    Hi, I need the help with the same problem,

    Well I know that Power is equal to P = 1/2 (u)(w)^2(A)^2(v). And when string is doubled the tension stays the same and length is reduced by half and the mass per unit length is increased by two. So the new eqution becomes: P = 1/4(u)(w)^2(A)^2(v). Is this a right answer? Or should I have done it somehow differently? Does v changes as well or stays the same?

  6. Feb 3, 2006 #5

    That's wrong.. replace v by another equation and start from there.. the rest will just follow through.. Isn't your assignment due today at 1?
  7. Feb 3, 2006 #6
    is due at 1pm or 9am?

    Anyway what I got when string is doubled is

    aplitude = A/2
    Mass per unit length = 2u
    speed =(T/2u)= 2^-0.5 v
    angular frequence =2pi/9T/2) = 4pi/T = 4pi f
    period = T/2
    tension =4
    P 1/2 (2u) (2pi f)^2 (A/2)^2 (2^-0.5 v) = u 16 (pi f)^2 (1/4) A^2(2^-0.5 v) = (2^-0.5)( u)(w^2)(A^2)(v)
  8. Feb 3, 2006 #7
    you are making your life complicated... this question is doable according to your prof. You are thinking too hard.. it's a really simple question. you are messing with too many variables. just think about what the doubling is affecting.. sorry I cannot help.. I have class to get to.
  9. Feb 3, 2006 #8


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    Staff: Mentor

    I agree. I don't think the half-length thing is part of the solution. The important thing is that the string is *doubled*. Hint -- is there a difference between doubling the string and running two separate strings? Unless you braid the two strings or something, I would think not. And if not, then how much more power can you transmit using two separate strings....?
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